Continuity circuits for detecting access disconnection

ABSTRACT

A monitor for an extracorporeal therapy access site is disclosed. The monitor includes a bandage atop or adjacent the access site and a sensor for monitoring the bandage. The bandage includes a layer of polymer that expands when wetted with blood. The expansion causes a break in continuity of the sensor, or in an alternate embodiment, causes a sensor to cease detecting a target. When the break occurs, the control circuit monitoring the bandage sends a signal that a break has occurred, and a remote monitor then takes appropriate action, such as ceasing therapy, sending an alert, or sounding an alarm. In another embodiment, connecting wires in a continuity circuit are held apart by a polymer that dissolves when contacted by blood. If a leak occurs and a small portion of the polymer dissolves, the wires make contact, thus detecting a blood leak.

BACKGROUND

The invention is in the field of medical treatments generally andpatient vascular access systems. The present invention relates toembodiments of a method and a system for detecting blood leakage duringextracorporeal blood treatment or other medical procedure.

The maxim of “first, do no harm,” may be a good summary of theHippocratic oath required of doctors and practiced by medicalprofessionals. Nowhere is this principle required more than in modernmedicine. With patients living longer, there are more extendedtreatments and more frail patients than ever. Such patients are indanger from complications that can arise from continuing therapeuticprocedures, and even from diagnostic procedures, that are necessary fortheir continued care. Treatments involving extra-corporeal bloodtreatment are clear examples.

The most obvious danger is infection, but the harm caused by infectioncan be overcome by not re-using even supposedly-sterile devices and bydiligent attention by the patient himself or herself, and by care giversattending to the patient. Other dangers also arise, but, likeinfections, have been difficult to eradicate. One of these dangersarises in blood treatment procedures in which the blood of a patient isphysically removed from the patient for treatment, and then returned,all in the same procedure. Removal and return of blood is practiced inhemodialysis, for those persons whose kidneys do not function well.Other procedures, such as apheresis, involve removing blood from apatient or a donor to separate blood platelets or plasma from the redblood cells and then returning the red blood cells to the patient ordonor, as described in U.S. Pat. Nos. 5,427,695 and 6,071,421.

The extracorporeal medical treatments described above require that theblood be removed for treatment and then returned. This requires accessto the patient's vascular system, from which blood is removed and towhich blood is then returned. If a “batch” treatment is used, that is, aquantity of blood is withdrawn, treated and returned, only a singleneedle is used. Each batch of such treatment is typically short, and thetreatment is attended by a medical professional at a clinic or hospital.A variation on the batch treatment is a “batch” continuous method inwhich only a single needle is used. There are distinct withdraw andreturn phases in a batch continuous process. During the draw phase,blood is processed and additional blood is sent to a holding containerto be processed during the return phase. In the return phase, blood isprocessed from the holding container and then returned to the patient ordonor through the single needle. Other treatments are continuous, suchas the platelet separation discussed above, or dialysis treatment, andmay require a duration of several hours or even overnight.

Continuous treatments require two needles, or access points, one forwithdrawal of blood and one for return. The withdrawal site is normallyan artery, and a needle and a pump are used to provide the blood to thetherapeutic machine. It is relatively simple to detect a problem withdrawal, for instance, if the withdrawal needle is dislodged, usingconventional air sensor technology. Detecting a problem in the return ofthe blood to the patient is more difficult. The return line typicallyincludes a needle with venous access. If the return line is dislodged,the blood is not returned to the patient's vascular system, but maycontinue to be pumped and may accumulate near the patient. Depending onthe pumping rate of the blood and the time for treatment, this couldhave life-threatening effects on the patient within a very short periodof time.

Accordingly, a number of apparatuses have been devised for detectingneedle dislodgement, especially venous needle dislodgement. An exampleis U.S. Pat. Appl. Publ. 2006/0130591. In a device according to thisapplication, a venous needle is equipped with a photosensor and iscovered with an opaque patch. This device would not send a signal or analarm if the needle begins leaking or is only slightly dislodged. Forexample, the photosensor could still fail to detect light because theneedle has not been dislodged sufficiently to expose the photosensor tolight. In addition, this method requires ambient light and would thusnot be suitable for patients that cover their arm with a blanket or whoperform nocturnal dialysis while sleeping in a dark bedroom.

Numerous other techniques have been devised, many of them depending on aflow of blood causing conductivity between two electrodes or two wires.What is needed is a better way of quickly detecting dislodgement of avenous or other needle from a patient, so that inadvertent loss of bloodand harm to the patient is avoided.

SUMMARY

One embodiment is a method for detecting blood leakage. The methodincludes steps of furnishing a pad with an expandable polymer layer anda sensor, placing the pad near an access site for an extracorporealblood therapy, taking an initial reading of the sensor, monitoring theaccess site by taking additional readings of the sensor during anextracorporeal blood processing therapy, and sending a signal if areading of the sensor is consistent with expansion of the expandablepolymer layer and a break of continuity of the sensor.

Another embodiment a method of detecting a fluid. The method includessteps of providing a fluid conveyor comprising at least one outer layerand a hydrophilic inner layer, the hydrophilic inner layer configured towick blood, placing the fluid conveyor near an extracorporeal therapyaccess site, monitoring a sensor to detect a presence of blood in thefluid conveyor, and sending a signal to a monitoring circuit if blood isdetected.

Another embodiment is an access disconnect detector. The accessdisconnect connector includes a pad having an expandable layer, and adetection circuit mounted near or atop the pad, wherein the pad isconfigured for placement adjacent an extracorporeal therapy access site,the expandable layer is configured for expanding upon contact withblood, and the detection circuit is configured for wirelesscommunication with an extracorporeal therapy machine or a controller incommunication with the extracorporeal therapy machine.

Another embodiment is an access disconnect detector. The accessdisconnect detector includes a fluid conveyor comprising at least oneouter layer and a hydrophilic inner layer, the hydrophilic inner layerconfigured to wick blood away from an extracorporeal therapy accesssite, a detector for detecting the blood within the fluid conveyor, anda control circuit in operable communication with the detector, whereinthe detector is configured to detect blood in the fluid conveyor and thecontrol circuit is configured to send a signal to alert a user or acaregiver of a presence of blood.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a prior art access site;

FIGS. 2-3 depicts a first embodiment of an expanding pad with a sensor;

FIG. 4 depicts a circuit for use with the first embodiment;

FIG. 5 depicts a second embodiment of an expanding pad with a sensor;

FIG. 6 depicts a third embodiment of an expanding pad with sensors;

FIG. 7 depicts a method of using an expanding pad to detect leakage ofblood at an access site;

FIG. 8 depicts an additional embodiment, in which a tubular conveyor isplaced between an access site and a detector;

FIG. 9 depicts another embodiment of a pad with a sensor;

FIG. 10 depicts a another embodiment of a pad with a continuity sensor;and

FIG. 11 depicts several simple logic circuits for determiningcontinuity.

DETAILED DESCRIPTION

Embodiments of the present invention are useful for monitoring an accesssite in which a patient receives extracorporeal blood therapy, such as aperson undergoing hemodialysis with a hemodialysis machine. An exampleof such a situation is depicted in FIG. 1, which depicts a patient Pundergoing hemodialysis with a hemodialysis machine H. The patient isconnected to the hemodialysis machine with tubing lines L connected toan arterial access site A and a venous access site V. Venous access siteneedle V_(n) is depicted. Other extracorporeal treatments are alsocontemplated, such as apheresis.

Expanding Bandage and Sensor Circuit

A first embodiment is depicted in FIGS. 2-3. In FIG. 2, a top view of anaccess site A is depicted, with a bandage 10. The bandage is placedadjacent access site A, so that the bandage is very close to thepenetration made by the needle into the arteriovenous fistula commonlyused for dialysis in these situations. Venous needle 24 is supported andmounted on the patient by needle mount 22, to which is connected venoustubing 26. The needle mount is typically taped onto the patient torestrain the needle during treatment and keep it reliably in place. Thebandage, as seen, includes a continuity sensor 18 and a control circuit40 atop the bandage. The continuity sensor 18 and control circuit arenot limited to the top layer, and indeed may be placed under the topsurface of bandage 10, in order to protect sensor.

FIG. 3 depicts a side perspective view of the bandage. The bandage ismade from several layers. The first layer 12 is an adhesive to restrainthe bandage on the patient. The next layer 14 should also be adjacentthe patient. Layer 14 is made from a polymer that expands upon wetting,and especially upon wetting with blood. An optional top layer 16provides a support for continuity sensor 18. Continuity sensor 18 may bea thin wire, a frangible piece of metal, a thin metallic tape, or anyother device useful for maintaining continuity across the top of thebandage during the therapy session. The center portion of layer 14 ismade thicker in the center, so that when blood is detected, theexpansion of the bandage is non-uniform and is greater in the center,thus causing the continuity sensor 18 to break.

As noted, the expandable or expanding layer is non-uniform, asymmetric,so that upon contact with blood an asymmetric expansion takes place. Theasymmetry may be accomplished as shown, with the center portion of thepad thicker, and therefore capable of much greater expansion than thesides. Other configurations may be used, such as layer that expands onlyon one side, left or right, or front or back, rather than the otherside. Still other embodiments could use an inner annular portion with agreater expansion rate than an outer portion, or vice-versa.

The expanding polymer may be one of many polymers that have beendeveloped for this expansion property. Many expanding polymers have beenused for medical purposes, such as outlined in U.S. Pat. No. 6,183,436,which discloses uses of such polymers as tampons in body cavities. Amongothers, materials such as polyvinyl alcohol, reaction products ofpolyvinyl alcohol and aldehydes, cellulose and cellulose derivatives,polyurethane, and like sponge materials. Another disclosure of suchmaterials is made in U.S. Pat. No. 6,112,380, which discloses manypolymers that may be compressed and then are capable of expandinggreatly when wetted with water, blood, or other moisture. Thesematerials include starch grafted poly(acrylic acid), a starchderivative, a cellulose derivative, foam, a polymer with asuperabsorbent agent (a superabsorbent polymer), poly(vinyl alcohol),poly(alkyl amine), poly(acrylamide) amine derivative, a hydrogel,poly(acrylic acid), microbial cellulose, poly(vinyl pyrrolidone),polyurethane, polyester, polyamide, polyimide, or combinations and/orsalts thereof. The collapsible and expandable material is generally veryporous. Superabsorbent polymers typically include those made frompoly(acrylic acid). Other materials that may be used includepoly(ethyleneoxide), poly(caprolactone), and poly(lactic-co-glycolicacid) (PLGA). Any other medically suitable material that has a suitableexpansion rate may be used.

As noted above, one of the problems with extracorporeal therapy isdislodgement of the needle, in spite of the care taken during placement.The problem may be more understandable, given the very long nature ofsome hemodialysis therapy sessions, including overnight sessions inwhich a patient may move considerably. Thus the need for a detectioncircuit. In this embodiment, when the needle becomes dislodged, bloodwill flow from the access site into the bandage, and in particular, intothe lowest bandage layer 14, the polymer that expands when wetted. Whenthe polymer expands, and thus layer 14 expands, no provision is made forthe expansion of to layer 16 or the continuity sensor 18. Thus, thedelicate sensor 18 splits apart upon expansion of layer 14, alertingcontrol circuit 40.

Circuit 40 is designed to monitor the health or continuity of sensor 41.control circuit 40 includes a control module 43, which maintains acontinuity check on sensor 41, using a voltage check circuit 42, oralternately, a current or resistive reading across the sensor. Thecontrol module includes logic such that when there is a change in thecontinuity of sensor 41, the control module 43 detects the change andthe communications module 44 communicates the change. The controlcircuitry may include a microprocessor to monitor the resistance orvoltage drop across sensor 41. Alternately, the control circuitry maysimply include an oscillator and timing circuit to periodically checkthe resistance across the sensor, and using, for example, digital logic,determine when the continuity has been broken and send a signal to thateffect via the communications module. Integrated circuits with a simplemicrocontroller are now sufficiently inexpensive that a very reliable,disposable or single-use circuit can be made with such microcontrollers.However, there are other options, especially with digital circuits, thatcan also be put into an integrated circuit that does not necessarilyrequire a microcontroller. An example is a suitable combination of AND,NAND, OR and NOR circuits, as depicted in FIG. 11 When the condition ofcontinuity across sensor 41 fails, the logic dictates that a signal besent to a remote controller to alert the patient or a caregiver of thefailure.

The communications module sends signals indicative of its findings orreadings to a remote receiver 46. One module that works is a wirelessmodule in accord with ZigBee/IEEE 805.15.4. This is a standard for avery low power radio system with a very limited range, about 10-20 feet.Modules made in accordance with this standard may be purchased fromMaxstream, Inc., Lindon, Utah, U.S.A., Helicomm, Inc., Carlsbad, Calif.,U.S.A., and ANT, Cochrane, Alberta, Canada. The module is very small,and may be about 2 cm square (about 1 inch square), and about 3 mm thick(⅛ inch). The remote receiver may be part of a therapy machine, or maybe a stand-alone circuit for receiving the signals and then alerting thepatient or caregiver by with a local output device, such as a speaker 47or a video screen 48. The monitor may also connect via landline 49, suchas to a hospital or clinic information system or other computer orcommunication system.

The control circuitry also includes a battery 45 to power the circuit.The sensor, the control module and the circuitry contained therein, aswell as the communications module 44 and a battery 45, are very small soas to fit comfortably atop the bandage. As noted, all the above, exceptfor the battery and the sensor, may be integrated into a microcircuit.The communications module may be wireless as shown in FIG. 4, requiringno harness, cord or cable connection to the patient. Alternately, a cordor cable could be used, which may or may not obviate the need for thebattery.

There are many other ways to detect expansion of the expanding polymer.For example, a top view of another sensor pad 50 is depicted in FIG. 5.Sensor pad 50 includes the same construction shown earlier, a firstexpanding layer intended for placement against the skin of the personnear the access site and a barrier layer which may act as a support fordetection components atop the pad. In this instance, the top layer 51 ofthe sensor pad also includes a proximity sensor 53 and a target 54. Solong as the sensor detects the target, the pad is presumed to be intactand the access site working properly. If the sensor does not detect thetarget, it may be because the expanding layer has contacted blood, hasexpanded, and has caused a split in the sensor pad. The top layer may beprovided with a split or a perforation 52 to ease the separation of thesensor from the target in case of an expansion.

Control circuits similar to those already described are used with thisembodiment. In this instance, a loss of continuity is not limited tosimple electrical conductivity, but also means loss of the detection ofthe target by the sensor. Proximity sensors include, but are not limitedto, capacitance sensors, inductance sensors, hall-effect sensors, and soforth. The target may be any small device that is easily detected by theproximity sensor, such as a small piece of steel, a small magnet, andthe like.

Yet another embodiment is disclosed in FIG. 6. In this instance, theneedle mount 60 is equipped with two targets 61, on either side of theaccess needle. The sensor pad 63 is constructed as above, but now hastwo proximity sensors 64 for detecting the targets. Control circuitry 65may be similar to that described for the previous embodiments, or may bedifferent, so long as the circuitry is capable of detecting the targetsand noting and communicating the loss of detection of the targets whenthe absorbing layer swells and lifts one or both of the proximitysensors 64 out of range of the targets. The circuitry for the proximitysensors may be set for as sensitive or as rough an adjustment asdesired. That is, patient move during long therapy sessions. Even thoughthe needle and the pad are firmly taped down, they will still move.Experience with a particular patient, perhaps a very controlled andreliable patient, may show that a 10% change in detection strength issufficient for dislodgement to have occurred. With a different patienthowever, who may be very restless, a 50% change in signal may notindicate that a leak has occurred. The control system is able toaccommodate these different situations by accommodating differentsetups.

One embodiment is a method of using the absorbent pad to detect accessdisconnection and a blood lead. This embodiment is disclosed in FIG. 7.In one step, an expanding pad with a sensor is furnished 71, the sensorconfigured for placement near an access site. The access needle isplaced into the access site and the sensor is placed 72 adjacent oragainst the needle mount. The sensor on the pad is detected 73. Inalternate embodiments, the sensor detects the target or targets on theneedle mount. The sensors are monitored 74 during therapy to insure thata blood leak does not occur, and also, with some embodiments, thatneedle dislodgement does not occur. If continuity is broken, as in someof the embodiments, or if a sensor no longer detects its target, asignal is sent 75. The signal may cause the therapy machine to shut off,that is, to stop 76 pumping blood from the patient. In otherembodiments, the signal is an alert to the patient or caregiver. Inother embodiments, an alarm, such as an announcement on a speaker, maybe sent.

Rate-Controlled Detection

As noted above, the quickest detection of blood is achieved by anexpanding bandage placed directly adjacent the access site. Anotheraspect of the present invention concerns situations in which theexpanding bandage cannot be placed as closely or as conveniently asdescribed above, or a situation in which it is desired to remove thebandage a short distance away, such as 2-5 cm. This situation occurswhen the access site has a small amount of blood or other fluid, such asbetadene, which would trigger false alarms from other sensors, such thesort of continuity sensors described in U.S. Pat. No. 6,445,304 and U.S.Pat. No. 6,979,306. In these situations, a minimum amount of fluid, suchas blood, is present, often for a period time, before the fluid canpresent to the sensor. In other situations it may not be possible toplace the entire bandage adjacent the site, but it is possible to placea smaller object, such as a sensor inlet tube, into the space available.

This situation is depicted in FIGS. 8 and 9. In FIG. 8, an access site80 includes a penetrating needle 81, which is preferably not dislodgedduring treatment or therapy. In the event of dislodgement, however, adistal end of a fluid conveyor 82 has been placed in the limited spaceavailable at the access site. Fluid conveyor 82 is connected at itsproximal end to a moisture detector 87. Moisture detector 87 may be anysuitable moisture detector, such as a capacitance sensor or conductivitycircuit. Many such detectors are disclosed in U.S. Pat. No. 7,147,615,assigned to the assignee of the present patent, and which is herebyincorporated by reference in its entirety. As noted above, the conveyoris typically 2-5 cm long, but other lengths may be used, such as 1-10cm. In one embodiment, the conveyors are manufactured at one length andare trimmed by cutting to the desired length.

Fluid conveyor 82 includes an outer shell 83 with a plurality ofapertures 84 through the shell, and also includes an inner packing 85.The outer shell is made from a hydrophobic material, such aspolyethylene, polypropylene, FEP (fluorinated ethylenepropylene), orPTFE (polytetrafluoroethylene). These materials will make a durableouter shell or covering. In some embodiments, the conveyor is made inthe shape of a collapsed bellows, like some soft-drink straws, so thatit is easily formed into a shape for the convenience of the patient. Theinner packing 85 is hydrophilic material that is capable of wickingmoisture and blood, and conveying the blood from the distal end of theconveyor to the proximal end, where the blood will be detected by themoisture detector 87. Hydrophilic materials include cotton, cellulosics,polyvinyl alcohol (PVA), and polyesters. The packing should be in a formamenable to wicking, such as a foam, a loose packing material, a sponge,or a staple (short fiber) material, such as cotton wool, cotton balls,or other loose, absorbent material. The hydrophobic material on theoutside, even when apertures are present, helps to prevent other fluidsor materials, such as betadene or other antiseptic, from entering theconveyor, thus restricting use of the conveyor, to the greatest extentpossible, for the fluid of interest, typically blood.

If a needle dislodgement occurs, blood will leak onto the access sitearea and will be absorbed by the fluid conveyor 82 and wicked throughthe inner packing 85. The wicking will transport the blood through theconveyor until the blood is detected by moisture sensor 87. The moisturesensor, a conductive, capacitive, or other moisture sensor, will send asignal via its connecting lines 88 to a controller or other remotedevice to alert the user that blood has been detected. In otherembodiments, sensor 87 may be part of a wireless circuit for monitoringthe patient during the therapy procedure, such as the monitor andcircuit depicted in FIG. 4. The wicking process will take longer than ifsensor 87 were directly mounted near the access site. This is desirablein the situations described above in which a part of the capacity of theconveyor has already been used for small amounts of blood that werepresent at the access site when hemodialysis began. This small delay isthus desirable to prevent false alarms.

In order for fluid conveyor 82 to work properly, the blood that passesthrough the conveyor should not clot. This can be arranged by addinganti-coagulant to the packing material. Examples of anti-coagulantmaterial include heparin, acid and citrate dextrose (ACD). The amount ofanti-coagulant needed depends on the packing material, the length of thetherapy, the evaporation rate of the anti-coagulant, the temperature ofthe conveyor, and many other variables. Other anti-coagulants can beused, such as any medication with acceptable use as a blood thinner thatwill not be applied to the vascular system of the patient.

Another situation using a patch 91 with hydrophilic and hydrophobiccomponents is depicted in FIG. 9. This embodiment is also useful inpreventing false alarms Patch 91 is placed over access site 90 toprotect and monitor the site and to insure that no leakage or accessdisconnect occurs, while allowing for the presence of very small amountsblood or fluid in a quiescent or non-accumulating manner. The patchincludes a top layer 92 of hydrophobic material, to keep moisture awayfrom entering the site. Middle layer 93 includes a hydrophilic filler,as discussed above, to wick moisture from the source to the sensor 97,no matter where on or in the patch the sensor is located. Bottom layer94 is porous, i.e., includes a plurality of apertures for admittingmoisture or blood for detection by sensor 97. Bottom layer 97 is alsomade from a hydrophobic material. Sensor 97 is connected to a remotemonitor or control circuit by cable 98, wherein remote may mean aslittle as a few feet or a meter away. When blood is detected by thesensor, the sensor control circuit detects the change in the sensorreading and takes appropriate action, such as to alert a user or acaregiver. In other embodiments, sensor 97 may be part of a wirelesscircuit for monitoring the patient. An example is the monitor andcontrol circuit depicted in FIG. 4.

Dissolving Insulator

In another embodiment, connecting wires in a continuity circuit are heldapart by a polymer that dissolves when contacted by blood. Anotherembodiment uses a multi-layer pad 100 with a continuity detector, asshown in FIG. 10. This embodiment includes a top layer 101, which may beany medically acceptable cover, such as polyethylene, nylon, cotton, andthe like. To top layer 101 is adhered a middle layer 103 in which areembedded one or more electrically-conductive wires 104, forming aninterconnected wire network. Wires 104 are desirably connectedelectrically so that when one of the wires 104 touches a wire in thesecond network of electrically-conductive wire network 105 beneathmiddle layer 103, the two networks are electrically connected. Belowsecond network 105 is a bottom cover layer 106.

The first wire network 104 is embedded within a material that dissolveswhen it wets blood. There are many examples of such materials, asdisclosed in U.S. Pats. No. 4,501,828, 4,499,214, and 5,332,524, each ofwhich is hereby incorporated by reference, as though each page andfigure were set forth explicitly herein. These documents teach numerouspolymer materials that may be prepared and which dissolve upon contactwith water. These materials include polyethylene oxide, polyacrylamide,polysaccharides (which may be sugars), and salts of these materials.These materials have also been found to dissolve upon contact withwater, and they will also dissolve on contact with blood.

The wire is prepared and the dissolving polymers are formed around thewires to form insulated-wire layer 103. A second layer of wires 105 isprepared and is placed adjacent the insulated-wire layer 103. Thepolymer insulation prevents contact between the wires of layers 103 and105. Bottom layer 106 insulates the second layer of wires 103 andprotects the wires from inadvertent contact. In one embodiment, apressure-sensitive adhesive 102 is used to removably adhere cover 101 tothe insulated wire layer.

In use, the top layer 101 may be peeled away from insulated wire layer103, and the insulated wire layer placed near the access site, with thepad secured by adhesive tape and with layer 106 facing away from thepatient. If an access disconnect occurs, or if the site leaks blood, theblood will dissolve the dissolving polymer and one or more of the wires104 will contact one or more of wires 105, thus completing a connectionbetween the two sets. Circuits such as those described above may be usedto monitor the conductivity or resistance between the two sets of wires.As one example, bundles of very small Litz wire may be used.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A method for detecting blood leakage, the method comprising:furnishing a pad with an expandable polymer layer and at least oneproximity sensor; placing at least one target near an access site for anextracorporeal blood therapy; placing the pad near the access site sothat the at least one proximity sensor detects the at least one target;taking an initial reading of the at least one proximity sensor;monitoring the access site by taking additional readings of the at leastone proximity sensor during an extracorporeal blood processing therapy;and sending a signal if a reading of the at least one proximity sensorindicates an expansion of the expandable polymer layer and a decreasedproximity of the at least one proximity sensor to the at least onetarget.
 2. The method of claim 1, further comprising sending adislodgement signal if a reading of the at least one proximity sensorindicates loss of detection of the at least one target when theexpandable polymer layer of the pad expands and lifts the at least oneproximity sensor out of range of the at least one target.
 3. The methodof claim 1, further comprising sending an alert or sounding an alarmwith a local output device.
 4. The method of claim 1, wherein asensitivity of the at least one proximity sensor and the at least onetarget is adjustable.
 5. The method of claim 1, wherein the at least oneproximity sensor is selected from the group consisting of hall-effectsensors, capacitance sensors, and inductance sensors.
 6. The method ofclaim 1, further comprising wicking blood from the access site using afluid conveyor with a hydrophilic layer.
 7. A method of detecting afluid, the method comprising: providing an elongated tubular fluidconveyor having an end distal relative to an extracorporeal therapyaccess site and an end proximal relative to the extracorporeal therapyaccess site, the elongated tubular fluid conveyor comprising at leastone outer layer and a hydrophilic inner layer, the hydrophilic innerlayer comprising an expandable polymer layer; placing the proximal endof the elongated tubular fluid conveyor near the extracorporeal therapyaccess site; monitoring a sensor arranged at the distal end and not atthe proximal end of the elongated tubular fluid conveyor to detect apresence of blood in the elongated tubular fluid conveyor; and sending asignal to a monitoring circuit if blood is detected by the sensor. 8.The method according to claim 7, wherein the hydrophilic inner layer isconfigured for absorbing and/or wicking blood.
 9. An extracorporealtreatment system comprising: an extracorporeal therapy machine; acontroller in communication with the extracorporeal therapy machine; andan access disconnect detector including a pad having an expandablepolymer layer, and a detection circuit mounted near or atop the pad, thedetection circuit including at least one proximity sensor, wherein thepad is configured for placement adjacent an extracorporeal therapyaccess site, the expandable polymer layer is configured for expandingupon contact with blood and carrying at least one target, and thedetection circuit is configured to send a wireless communication signalto the extracorporeal therapy machine or to the controller incommunication with the extracorporeal therapy machine when a reading ofthe at least one proximity sensor indicates an expansion of theexpandable polymer layer and a decreased proximity of the at least oneproximity sensor to the at least one target.
 10. The extracorporealtreatment system according to claim 9, wherein the detection circuitcomprises a continuity circuit, a controller, and a wirelesscommunications module.
 11. The extracorporeal treatment system accordingto claim 9, wherein the at least one target comprises a thin metallicobject.
 12. The extracorporeal treatment system according to claim 9,wherein the detection circuit includes two proximity sensors and the atleast one target includes two targets.
 13. The extracorporeal treatmentsystem according to claim 9, further comprising a local output devicefor raising an alert or sounding an alarm.
 14. The extracorporealtreatment system according to claim 9, further comprising an accessneedle attached to an access mount, wherein the at least one target ison a mount.
 15. The extracorporeal treatment system according to claim9, wherein the expandable polymer layer is made from polyvinyl alcohol,a polyvinyl alcohol derivative, acrylic acid, an acrylic acidderivative, or a combination thereof.
 16. The extracorporeal treatmentsystem according to claim 9, wherein the extracorporeal therapy machineis a hemodialysis machine and further comprising the hemodialysismachine.
 17. The extracorporeal treatment system according to claim 9,further comprising a fluid conveyor with a hydrophilic layer placedbetween the access site and the pad.
 18. The extracorporeal treatmentsystem according to claim 9, wherein the expandable layer is asymmetric.19. The method of claim 1, wherein the at least one target is metallicor magnetic.
 20. The method according to claim 7, wherein thehydrophilic inner layer includes an additive anticoagulant.
 21. Themethod according to claim 20, wherein the additive anticoagulant isselected from the group consisting of heparin, acid, citrate dextrose,and blood thinner medication.
 22. A method for detecting blood leakagecomprising: (i) furnishing a pad with an expandable polymer layer and atleast one proximity sensor; (ii) enabling the placement of at least onetarget near an access site for an extracorporeal blood processingtherapy; (iii) enabling the placement of the pad near the access site sothat the at least one proximity sensor detects the at least one target;(iv) enabling the taking of an initial reading of the at least oneproximity sensor after the placement occurs in (i) and (ii); (v)enabling the taking of additional readings of the at least one proximitysensor during the extracorporeal blood processing therapy; and (vi)sending a signal if a reading of the at least one proximity sensorindicates loss of detection of the at least one target when theexpandable polymer layer expands and lifts the at least one proximitysensor out of range of the at least one target.